1. Field
The invention relates to automated control systems for steam sterilizers and chemical sterilizers. More particularly, the invention pertains to control systems for determining the status of a sterilizer following power failure and controlling the operation according to the determined status.
2. State of the Art
Sterilizers using steam and/or chemicals as the sterilant are operated through a series of sequential steps in each operation cycle. Execution of these steps is typically controlled by a microprocessor control board with appropriate manual setting of sterilizing conditions and start/stop override options.
In the event of an extended power failure where the memory backup circuits are invalid, i.e. memory is erased, the control board is configured to initiate a purge upon restoration of power. The purge must be completed before the door lock is activated to the "open" position to avoid possible injury to the operator. The purge ensures that no steam or chemical vapors are present in the chamber before re-starting the sterilization cycle or opening the door. In the past, a purge was always necessary because there was no positive indication of the absence or presence of water or chemical sterilant in the sterilizer chamber following an extended power loss. Reprocessing of the load in the sterilizer required the initiation of a purge step to safely remove sterilant (if any) from the chamber. Efficient and effective sterilization requires close control of the sterilant quantity introduced into the sterilizer chamber. The quantity must be held within narrow limits. Excessive dosages of sterilant typically lead to longer cycle times because of slower heatup, extended vent and purge operations, etc. In addition, power requirements are increased, wastage of sterilant occurs, and the sterilizing process itself may be jeopardized.
Thus, the prior art uses a default purge step to ensure that the sterilizer chamber is free of sterilant and ready for use. The method is costly in terms of the extra time, energy and sterilant which it consumes.
The need remains for a method to indicate the status of the sterilizer chamber with regard to the absence or presence of sterilant, and using the method to eliminate non-necessary purges and to initiate necessary purges. The indication method must be reliable under extended conditions of line power loss.